Comparison of long-term progestin-based estrus synchronization protocols in beef heifers

Area of Science:

• Reproductive physiology in beef cattle
• Artificial insemination protocols
• Estrus synchronization

Background:

• Fixed-time artificial insemination (FTAI) requires effective estrus synchronization in beef heifers.
• Progestin-based protocols are commonly used to manage estrous cycles.
• Evaluating long-term efficacy and heifer response is crucial for FTAI success.

Purpose of the Study:

• To compare two progestin-based estrus synchronization protocols: melengestrol acetate-PGF(2α) (MGA-PG) and Show-Me-Synch.
• To assess the protocols' effectiveness in facilitating fixed-time AI in estrous cycling and prepubertal beef heifers.
• To evaluate estrous response, synchrony, and fertility rates associated with each protocol.

Main Methods:

• Two experiments were conducted involving beef heifers.
• Experiment 1 (n=99) compared MGA-PG and Show-Me-Synch protocols using HeatWatch estrus detection.
• Experiment 2 (n=396) further evaluated estrus distribution patterns with HeatWatch transmitters post-PGF(2α) administration.

Main Results:

• No significant differences in conception to AI, AI pregnancy, or final pregnancy rates were observed between protocols in either experiment.
• In Experiment 1, the MGA-PG protocol tended to reduce the variance in interval to estrus post-PGF(2α).
• In Experiment 2, the Show-Me-Synch protocol showed a greater estrous response (92% vs. 85%) and reduced variance in interval to estrus post-PGF(2α) compared to MGA-PG.

Conclusions:

• The Show-Me-Synch protocol favorably compared to the MGA-PG protocol regarding estrous response and synchrony.
• Both protocols resulted in comparable fertility rates, suggesting flexibility in program selection based on specific herd needs.
• Estrus synchronization programs are effective tools for facilitating fixed-time AI in beef heifers.